This invention pertains to computer systems and other information handling systems and, more particularly, to a Blade Center comprising a plurality of server Blades in which local drives, typically removable media drives, can be shared while maintaining a full-time device connection between the individual server blades and a respective I/O device interface which serves as a conduit to the drives.
When computer system servers are provided in close proximity in order to increase the density of servers in a given volume of space, it is common to share lesser-used resources such as CD-ROM, floppy, keyboard, video, and mouse. Attempts have been made to share such resources by electrically switching a resource to the server needing the resource. This has been accomplished by using a switch or a multiplexer.
While such switching tends to not produce problems in relatively stateless interfaces such as analog video, Applicants have discovered that interfaces having states which depend on prior states can be disrupted by the untimely switching, whether in or out, of the interface connection. USB is one such interface which has been discovered to be problematic when attempting to share a removable media drive such as a CD-ROM.
USB is an I/O bus having an asymmetric design. A single host-side controller is able to act as a master and connects to multiple devices directly or to hubs to extend the total number of devices connected to a single host. When hubs are used to extend the bus, the hubs are connected in a tree-like structure. Hosts include at least one hub and up to 127 devices may be connected to a single host, but the count must include the hub devices as well, so the total useful number of connected devices is somewhat diminished.
The untimely switching of a USB device on a USB interface can cause state machine errors in the USB host controller, USB hub, or USB device interface. Even where the switching is electronically controlled such that these errors are shunned, operating system drivers containing higher level state machines can be equally confounded by the switch. For example, it is known that copying the contents of a folder from an untimely switched USB drive can result in a copy operation wherein only a portion of the files in the folder are actually copied over. Although a warning message is displayed, the user is left with a logistically difficult situation: the drive is no longer accessible and the names of the missing files are unknown.
Another problem inherent to the switched design is that a switched drive cannot be shared amongst the different servers. Accordingly, should a network administrator desire to install a new version of Linux on all of the servers that have access to the shared drive, the administrator must wait for the complete installation to complete in order to begin installation on the different server. This increases the cost of maintenance which is known to be a significant factor in the purchase of a product.